This invention relates to improvements in the processing zone of a particulate material processor having a circumferentially directed flow of fluid to develop a circumferentially circulating turbulent toroidal bed of material within the processing zone.
Treatment of particulate material commonly uses a fluid but more particularly a gaseous stream. The particulate material may function as a catalyst, absorptive medium or as a source of reactants which react with or are treated by the fluid stream. It has been thought for some time that the best mode for treating beds of particulate material is to fluidize the bed with a gaseous stream. Fluidization of the bed usually results in the particulate material moving randomly in the bed and resembling a random motion similar to boiling water. Exemplary systems for fluidizing beds of material where the material is to be treated are described in U.S. Pat. Nos. 3,527,575; 4,067,118; 4,530,169; 4,970,804; 5,282,321 and 5,357,688. The fluidized beds of these references are of the standard upwardly expanded type which may optionally involve a swirling motion in the bed as developed by angled jets of air such as described in the above U.S. patents.
A vertically expanded annular bed of material is described in U.S. Pat. No. 5,033,205. The circulation of the particulate material in the annular bed is upwardly then outwardly for return to the lower air jet portion of the reactor chamber.
U.S. Pat. No. 4,479,920 describes an annular processing zone for a circumferentially circulating turbulent bed of material. The system is commonly sold under the trade mark TORBED(trademark) and has been used in a variety of particulate treatment applications such as metal ore treatment and roasting; catalytic particle treatment; drying of particulate matter; reacting particles with the gaseous stream; tablet coating; coffee bean roasting and the like. Although this type of annular processing zone is very effective and efficient in treating particulate material due to the uncontrolled random motion of the particles in the swirling turbulent annular bed of material there may be situations when not all particles in the bed are evenly treated and hence a variation in the quality of the final treated particulate product.
In accordance with an aspect of the invention it is desirable to provide an annular processing zone which provides for a predictable particle flow path both circumferentially of the processing zone and helically of the zone to ensure more uniform particle treatment for a given residence time.
In one of its aspects, the invention provides a process for bringing particulate material into contact with a moving fluid in an annular processing zone to create processed material. The zone has a base and the process includes generating a circumferentially directed flow of gas in the zone to develop a circumferentially circulating turbulent bed of particulate material within the processing zone. Particulate material is supplied to the processing zone so that the particulate material is circulated in the processing zone to provide a predictable particle flow path both circumferentially of the processing zone and helically of the zone. The flow path has the following characteristics:
(i) the flow of fluid is controlled to develop the circulating bed with a width between about 2% to 20% of the bed outer extremity diameter, an inner bed depth of less than 1% of the bed diameter, and an outer bed depth between about 2% to 5% of the bed diameter; and
(ii) the flow of fluid is directed at an angle relative to the base of the processing zone in the range of about 100 to 450; and discharging particulate material from the processing zone after processing in the processing zone.
In another of its aspects, the invention provides apparatus for carrying out the process.